CVE-2026-13221

Perl versions through 5.43.9 produce silently incorrect regular expression matches when an alternation of more than 65535 fixed string branches is compiled into a trie in Perl_study_chunk. When such branches are combined into a trie, the delta between the first branch and the shared tail is stored in a 16-bit field. A branch count above 65535 overflows the field, and the trie's match decision table is truncated with no warning or error. A pattern of this shape produces false positive matches (matching strings it should not) and false negative matches (failing to match strings it should). When such a pattern gates an access or filtering decision, the result is wrong.

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• perl https://lists.security.metacpan.org/cve-announce/msg/41780104/ https://github.com/Perl/perl5/issues/23388 Introduced with: https://github.com/Perl/perl5/commit/acababb42be12ff2986b73c1bfa963b70bb5d54e (v5.37.10) Fixed by: https://github.com/Perl/perl5/commit/03f74bbbd3a68350d926ee93d56ee4808c28c4c7 (v5.43.10)